Build your first app

The following pages teach you how to build a simple Android app. You’ll learn how
to create a "Hello World" project with Android Studio and run it. Then, you'll create a new
interface for the app that takes some user input and opens a second screen in the app.

But before you start, there are two fundamental concepts you should
understand about Android apps:

Apps provide multiple entry points

Android apps are built as a combination of components that can be invoked
individually. For example, an activity is a type of app component that provides a
user interface.

The "main" activity is what starts when the user taps your app icon, but you can take the user
straight into a different activity from other places, such as from a notification or even from
a different app.

Other components such as broadcast receivers and services also allow your app
to perform background tasks without a user interface.

After you build your first app, learn more about the other components
at App Fundamentals.

Apps adapt to different devices

Android allows you to provide different resources
for different devices. For example, you can create different
layouts for different screen sizes. Then the system
determines which layout to use based on the current device's screen size.

If any of your app's features need specific hardware, such as a camera, you can query whether
the device has that hardware at runtime and then disable the corresponding features if not.
You can also set some features as required
so Google Play won't allow installation on devices without them.